The present invention relates to a press for forming large-diameter heavy-gauge steel pipe and, more particularly, is directed to such a press for forming preformed U-shaped blanks into an O-shape.
In the art of forming heavy-gauge, large-diameter steel pipe, an old practice is to first cut an elongate flat steel blank, then form the balnk into a U-shaped cross-section in what is known as a "U-ing Press", then form the U-shaped blank into an O-shaped cross-section in what is known as an "O-ing Press", and finally weld and finish the confronting edges of the O-shaped blank. A recent example of such a technique may be seen in U.S. Pat. No. 4,148,426.
The purpose of the present invention is to provide a press which is capable of providing and withstanding the extremely high forces which are required for the forming of large-diameter heavy-gauge steel pipe. For example, such pipe might have a wall thickness of an inch, a length of from 30 to 40 feet, and an outside diameter of from 18 to 40 inches. The pressing capacity of the press could be in the range of 90,000 tons, the exact capacity depending upon the yield strength of the plate and the wall thickness of the pipe.
A number of problems are encountered in providing a press of the capacity with which the present invention is concerned. One of the main problems is that the press must be capable of providing the extremely high press forces (e.g., 90,000 tons), while not being subject to destructive eccentric loading at these extremely high forces. Eccentric loading can occur whenever the length of the pipe blank is less than the length of the press, since one or both ends of the press will then be more lightly loaded than the center of the press and, thus, tend to move faster than the center of the press. Another form of destructive loading of the press can result from elongation of the pipe during the pipe formation process. Absent some accommodation for this elongation, distortion of the pipe and/or the imparting of destructive forces of the press can result. Still another problem in providing extremely large presses of the type with which the present invention is concerned is the matter of providing hydraulic press operating cylinders capable of generating the forces required, while at the same time being economically feasible and of a size which can be accommodated.